1. Field of the Invention
The present invention relates to a temperature controller designed to maintain an optical-communication device at a constant temperature regardless of ambient temperature variations.
2. Description of the Related Art
In general, optical-communication devices such as a laser diode and an Arrayed Wavelength Grating (hereinafter referred to as AWG) which are used in Wavelength Division Multiplexing (hereinafter referred to as WDM) are sensitive to ambient temperature variations. It is preferred that optical-communication devices as described above employ a temperature controller to maintain a constant temperature, so as to restrict the wavelength transition of a transmitted optical signal and stabilize the wavelength of a demultiplexed optical signal in a W DM optical transmission and a WDM-PON (Passive Optical Network) transmission, thereby realizing a stable optical system free from interference from adjacent optical channels.
FIG. 1 is a block diagram showing the construction of a temperature controller in a general optical-communication device, in which the temperature controller includes a temperature sensor 10, a temperature-comparison section 20, a PID control section 30, a current-supply section 40, and a temperature-control section 50.
The temperature sensor 10 detects the current temperature of an optical-communication device 60 such as the AWG. The temperature sensor utilizes a thermistor, or Pt-resistance temperature detector, whose resistance varies according to temperature variations. The Pt-resistance temperature detector has a Positive Temperature Coefficient (hereinafter referred to as PTC) in which its resistance increases as the temperature rises. The thermistor has a PTC or Negative Temperature Coefficient (hereinafter referred to as NTC) according to the composition of the materials thereof.
The temperature-comparison section 20 compares a predetermined temperature with a current temperature and generates an error voltage Verr corresponding to the difference between the predetermined and current temperature voltages. The temperature controller establishes the predetermined temperature by applying a voltage with a general-purpose microcontroller and a Digital-to-Analog Converter (DAC) or directly applying a reference voltage Vref. The temperature controller reads the resistance of the temperature sensor 10 attached to the optical-communication device 60, such as the AWG, converts the resistance into a current voltage Vcur, and then compares the current voltage Vcur with that of the predetermined temperature so as to obtain the current temperature. The compared error voltage is applied to the PID control section 20.
The PID control section 30 receives the error voltage from the temperature-comparison section, adjusts an output voltage so as to conform the current temperature to the predetermined temperature, and applies the output voltage into the current supply section 40. The PID control section may selectively use P-, PI-, PD-, PID-control circuits, and so forth according to temperature variation characteristics.
The current-supply section 40 amplifies the output voltage from the PID control section 30 into a high current using a power operational amplifier (hereinafter referred to as OPA) or a PWM (Pulse Width Modulation) driver, and supplies the high current to the temperature-control section 50.
The temperature-control section 50 controls the temperature of the optical-communication device 60, based upon the high current applied from the current-supply section 40. The polarity of the current applied to the temperature control section 50 is determined by the polarity of the error voltage Verr which is the difference between the predetermined and the current temperature voltages in the temperature-comparison section 20. If the error voltage indicates a positive voltage, a positive current is generated. If the error voltage indicates a negative voltage, a negative current is generated. Such a temperature controller may include a heater, a Thermo-Electric Cooler (hereinafter referred to as TEC), etc. In general, the TEC is in the form of a device for heating or cooling an object to be temperature-controlled, and it is used to maintain the temperature of a WDM laser diode. The TEC or heater is used for the AWG, in which the heater heats an object to be temperature-controlled regardless of the polarity of the applied current.
In the temperature controller having the above construction, it compares the current temperature voltage with the predetermined temperature voltage using an Instrument Amplifier (hereinafter referred to as IA) circuit so that any error can be amplified precisely via the OP amplifier and the differential amplifier using the OPA.
FIG. 2 is a diagram showing a construction of the temperature-comparison section of a temperature controller employed in a conventional optical-communication device. First, the case where the temperature-comparison section utilizes an IA and employs a Pt-resistance temperature detector as a temperature sensor will be described below.
The Pt-resistance temperature detector shows a PTC characteristic, that is a resistance variation according to the temperature, in which the resistance thereof is 100 Ω at 0° C. and increases by 0.385 Ω for each 1° C. rise in temperature.
In conversion of a resistance of the Pt-resistance temperature detector into a voltage, where it is supposed that a reference voltage Vref is 3V, a resistance R is 100 Ω, and a predetermined temperature is 70° C., a predetermined temperature voltage V1 is set as 1.678V and is inputted into an anode terminal of the IA 21 while a current temperature voltage is inputted into a cathode terminal of the IA 21. Then, an output-error voltage 22 of the temperature-comparison section is applied with a positive polarity into a heater or a TEC having a temperature-maintenance function with the positive polarity current at a current-supply terminal, so as to maintain a desired temperature.
Next, the temperature-comparison section may utilize a thermistor 51 having an NTC characteristic. The thermistor shows a resistance of 100 kΩ at 25° C. and approximately 14.6 kΩ at 70° C. Where R is 100 kΩ, the voltage of the set temperature is approximately 0.382V. The set temperature is inputted into the cathode terminal of the IA while the current temperature voltage is inputted into an anode terminal of the IA so as to supply the current to the TEC or heater through the PID control.
The current temperature voltage increases, approaching the predetermined temperature in the PTC sensor as set forth above, while the current temperature voltage decreases to approach the predetermined temperature in the NTC sensor. That is, the current temperature voltage is inputted into the anode terminal of the IA in the case of the PTC sensor but into the cathode terminal of the IA in the case of the NTC sensor thereby restricting application of the NTC and PTC sensors in a single PCB at the same time.